Assessing the Socio-Environmental Risk of Onsite Wastewater Treatment Systems to Inform Management Decisions.

Quantifying the risk that failing onsite waste treatment systems (OWTS), such as septic systems, present to human health and the environment is a key component in natural resource management. We integrated environmental and socio-demographic data to assess the potential environmental risk and environmental justice concerns related to septic infrastructure. We used this process to develop a framework that can be applied in other jurisdictions. We found only 8% of the registered OWTS presented potential environmental risk due to the topographic, hydrologic, or edaphic characteristics of their placement. In contrast, almost 70% of the OWTS presented potential environmental risk due to their age (25 years or older). Approximately 60% of the OWTS we estimated to be at risk from age or placement were found in census blocks with more than 30% of the population living below the poverty line, had a population that was more than 50% nonwhite, or was predominantly nonwhite and impoverished. Our work suggests that jurisdictions with limited information about septic infrastructure may be able to use geospatial data that they do have to predict the parcel-level locations of OWTS. These locations can then be used to inform environmental monitoring to proactively address environmental justice concerns.